Although exercise is widely regarded as a key component in obesity treatment, few individuals seem able to adhere to exercise programs over time. In response, efforts have focused on developing new approaches to physical activity that may appeal to sedentary overweight persons. For instance, is has been shown that accumulating multiple short bouts of vigorous exercise may enhance both exercise adherence and weight loss in overweight persons. Accumulating moderate-intensity activity throughout the day may offer comparable health and weight benefits as a traditional exercise program. Public health recommendations now include the option of accumulating 30 minutes of moderate-intensity lifestyle activity for health and well-being. While these two options offer a viable alternative to those who dislike or cannot sustain continuous vigorous exercise programs, it is unclear whether the flexibility of accumulating physical activity or the vigorous intensity of the exercise is responsible for improved weight loss and long-term adherence. The goal of this research is to extend our preliminary findings suggesting that moderate intensity lifestyle activity is an important and viable alternative to traditional structured vigorous exercise for obese dieting individuals. The primary specific aim of this project is to compare the effects of three modes of exercise on long-term weight regain. Participants will be 165 overweight men and women who are sedentary, but otherwise healthy. All participants will receive the same 16-week behavioral weight loss program and will be randomized to one of three exercise study conditions: 1) diet-plus-continuous bouts of vigorous aerobic exercise; 2) diet-plus-short bouts of vigorous aerobic exercise accumulated throughout the day; or 3) diet-plus-moderate intensity lifestyle activity accumulated throughout the day. By varying both the intensity and duration of exercise bouts, we can determine which type of exercise is associated with optimal outcomes one year later. Additional questions of interest include: 1. Does mode of exercise influence exercise adherence? 2. Does mode of exercise improve cardiovascular risk profiles similarly in all three conditions? 3. Does mode of exercise influence changes in body composition? 4. Does mode of exercise influence exercise enjoyment and exercise self-efficacy?